Call to undefined function – header

I had a mnior screwup last night. The installation initially went fine, and I’d customized two of my theme pages. Then a bunch of unrelated garbage got put into the same folder on the server, which I deleted. But since then, I’m getting this when i try to visit the index.php page:

Fatal error: Call to undefined function: get_header() in /home/fqhqtmx/public_html/content/channelblog/index.php on line 2

This is line 2 on the page:
<?php get_header(); ?>

The header file is in he same folder.

Here’s the blog link if necessary:

https://www.crncanada.ca/content/channelblog/

Any ideas?